Turbine casings for rotating machines, which radially enclose a flow passage along which the operating medium axially expands, producing expansion energy, and as a result of which a rotor arrangement is arranged, which is enclosed by the turbine casing and equipped with rotor blades, serve as a support structure for stator blades which project into the spaces between the stator blade rows which are attached on the rotor side. For construction and installation reasons, turbine casings are composed of at least two casing halves which are joined together via an axially extending parting plane in each case to form a uniform turbine casing. As a result of the split design in each case of the so-called upper and lower turbine casing halves, an installation-friendly fitting is possible of the turbine stator blades in the stator blade root recesses, which are provided in and along the turbine casing inner wall and around it in the circumferential direction, before the two turbine casing halves are joined together.
Furthermore, turbine casings which for installation reasons are not only composed of an upper and a lower turbine casing half but, moreover, are composed of at least two casing sections per turbine casing half, are of particular interest. Such a construction may be explained in more detail as representative of further turbine casing designs based on the example of a low-pressure steam turbine stage, as used for example in combined cycle power plants. Combined cycle power plants are power plants which provide a combined gas turbine and steam turbine cycle, i.e. the hot exhaust gases which issue from the gas turbine unit are used for steam generation and the steam which is generated in the process is used for operating suitable steam turbines stages, for example for operating a low-pressure steam turbine stage in this way. Combined cycle power plants of the above generic type can be taken for example from U.S. Pat. Nos. 5,199,256 or 4,519,207.
A cross-sectional view through the turbine casing of a typical low-pressure steam turbine is shown in DE 25 03 493 with reference to FIG. 1, which has a turbine casing which is composed of two times three parts. Thus, both the upper and the lower turbine casing half is composed of three casing sections which are axially joined together in each case, of which the center casing section together with an internally-disposed rotor arrangement includes a flow passage which conically widens axially on both sides. A casing end section is axially connected on both sides in each case to the ends of the center casing section, which casing end section is referred to as a blade carrier, particularly as a stator blade row is fastened to this in each case. The two casing end sections, which are axially connected by the face end to the center casing section in each case, are connected in a fixed manner via corresponding connecting constructions to the center casing section. The production of all the individual parts, of which the turbine casing described above is composed, is carried out within the scope of separate casting processes in each case so that each individual component requires a separate casting mold in each case which is used in separate casting processes in each case which are independent of each other. Such a procedure is not only time-intensive, and therefore cost-intensive, but furthermore requires a high-precision reworking of the individual casing sections in order to join them together in an accurately fitting manner to form a uniform turbine casing. The turbine casing of a low-pressure steam turbine is typically enclosed by a further casing, that is to say by the so-called outer casing, as this is described for example in DE 38 37 510 C2.